Amazon CloudWatch
User Guide

Create or Edit a CloudWatch Alarm

You can choose specific metrics to trigger the alarm and specify thresholds for those metrics. You can then set your alarm to change state when a metric exceeds a threshold that you have defined.

To create an alarm

  1. Open the CloudWatch console at

  2. In the navigation pane, choose Alarms, Create Alarm.

  3. For the Select Metric step, do the following:

    1. Choose a metric category (for example, EC2 Metrics).

    2. Select an instance and metric (for example, CPUUtilization).

    3. For the statistic, choose one of the statistics (for example, Average) or predefined percentiles, or specify a custom percentile (for example, p95.45).

    4. Choose a period (for example, 1 Hour).

    5. Choose Next.

  4. For the Define Alarm step, do the following:

    1. Under Alarm Threshold, type a unique name for the alarm and a description of the alarm. For Whenever, specify a threshold (for example, 80 percent of CPU utilization) and the number of periods. Alarm names must contain only ASCII characters.

    2. Under Additional settings, for Treat missing data as, select how have the alarm treat missing data points. For more information, see Configuring How CloudWatch Alarms Treats Missing Data.

      If the alarm uses a percentile as the monitored statistic, choose whether to evaluate or ignore cases with low sample rates. If you choose ignore, the current alarm state is maintained when the sample size is too low. For more information, see Percentile-Based CloudWatch Alarms and Low Data Samples.

                Treat missing data and Percentiles with low samples UI fields
    3. Under Actions, select the type of action to have the alarm to perform when the alarm is triggered.

    4. Choose Create Alarm.

You can also add alarms to a dashboard. For more information, see Add or Remove an Alarm from a CloudWatch Dashboard.

To edit an alarm

  1. Open the CloudWatch console at

  2. In the navigation pane, choose Alarms.

  3. Select the alarm, and then choose Actions, Modify.

  4. In the Modify Alarm dialog box, update the alarm as necessary and choose Save Changes.

To update an email notification list that was created using the Amazon SNS console

  1. Open the Amazon SNS console at

  2. In the navigation pane, choose Topics, and then select the ARN for your notification list (topic).

  3. Do one of the following:

    • To add an email address, choose Create subscription. For Protocol, choose Email. For Endpoint, type the email address of the new recipient. Choose Create subscription.

    • To remove an email address, choose the Subscription ID. Choose Other subscription actions, Delete subscriptions.

  4. Choose Publish to topic.